This invention relates generally to the field of telecommunications, and more particularly to a method and system for transporting synchronous and asynchronous traffic on a bus of a telecommunications node.
The Internet has dramatically increased the potential for data, voice, and video services for customers. Existing circuit-switched telephony systems, however, do not provide the foundation to support the growing need for bandwidth and new services required by both residential and business consumers. As a result, integrated access devices have been introduced to support Internet and related technologies as well as standard telephony service.
Integrated access devices often combine synchronous and asynchronous transport and switch functionality to multiplex data, voice, and video traffic together onto a single network. A time division multiplex (TDM) bus is used to transport voice and other synchronous traffic between the line cards and a switch core. Asynchronous transfer mode (ATM) traffic is transported between the line cards and the switch core on an ATM bus. At the switch core, traffic may be converted between TDM and ATM formats for high speed transmission on the network or for distribution to customer premises.
The ATM bus carries ATM traffic from various ATM interfaces, such as T1 UNI, DS3 UNI, and OC-3C UNI, to the switch core. On the ATM bus, cells are automatically assigned to available slots on demand to provide maximum throughput. Header information within the ATM cells provides necessary switching information to the switch core. Due to their asynchronous nature, ATM buses have traditionally been very limited to carrying ATM or packet-based traffic.
The present invention provides an improved method and system for transporting traffic on a bus of a telecommunications node that substantially eliminates or reduces the disadvantages and problems associated with previous systems and methods. In particular, the bus provides increased bandwidth over a node backplane and utilizes a bus format that is capable of transporting both synchronous and asynchronous traffic at high speeds and that facilitates switching at a switch core.
In accordance with one embodiment of the present invention, a bus for a telecommunications node includes a frame repeating at a defined interval and including a defined number of slots. Each slot includes a overhead portion identifying a type of traffic in the slot and the service traffic portion transporting traffic of the type. A first slot in at least one frame transports in a service traffic portion asynchronous traffic and routing information for the asynchronous traffic in the telecommunications node. A second slot in the frame transports synchronous traffic in the service traffic portion and has a location in the frame associated with routing information for the synchronous traffic in the telecommunications node.
More specifically, in accordance with a particular embodiment of the present invention, the bus may include a point-to-point link between the line card and a switch core in the telecommunications node. In this embodiment, each point-to-point link includes the frame repeating at the defined interval. The frame repeats at 125 microsecond intervals with each slot being 64 bytes in size. For a 64 byte slot the ATM cell may be a modified cell with the routing information omitting a header error correction (HEC) value originally received with the ATM cell.
Technical advantages of the present invention include providing an improved method and system for transporting traffic on a bus of a telecommunications node. In particular, the bus uses a repeating frame structure having a fixed number of time slots that are sized to accommodate an ATM cell plus required overhead and control information. As a result, the bus is capable of transporting both synchronous and asynchronous traffic at high rates. This allows an enormous degree of flexibility in operating the telecommunications node. In addition, transport and switch operations in the telecommunications node are simplified and costs of the node are reduced.
Another technical advantage of the present invention includes providing in-band control signaling between cards on the bus. In particular, the bus format supports a wide variety of control information and provides in-band signaling of back-pressure and transfer authorization signals. As a result, separate control lines between the line cards and switch core are not needed to control the transmission of traffic between the line cards and the switch core. Thus, costs of the node are further reduced.
Other technical advantages of the present invention will be readily apparent to one skilled in the art from the following figures, description, and claims.